Are propane or kerosene heaters SAFE to use in enclosed spaces if the heater is not vented to the outside air? I've always heard they were not safe if not vented outside. And for the garage under consideration here, cutting a vent hole in the wall does not seem like a good idea. Unless its an unattached garage building with no insulation so cutting a hole is real simple.. I would not want to cut holes in the walls of my attached garage. Thus the reason electric heaters are popular.